The Reds have played in the National League since 1890, although they trace their name to the Cincinnati Red Stockings, the first professional baseball team ever assembled, in 1869. The present team was founded in 1882 as a member of the American Association and has no direct relation to the first professional baseball team of the same name. They moved to the National League as a result of the Players League challenge of 1890, which put a rival team in the Queen City, known by its nickname Kelly's Killers; that team moved to the American Association in 1891 and disappeared along with the entire circuit at then end of that season. There was also a Cincinnati Red Stockings team, also sometimes called the Reds, that was a member of the National League from its inaugural season in 1876 until 1880, but that team is also not directly related to the present one. However, with Cincinnati being the home of the founding team of professional baseball, the National League would traditionally play its season opener in Cincinnati until the 2000s, while the American League opened in Washington, DC. If the history of baseball in Cincinnati prior to 1892 is somewhat convoluted, it is not the case since, as there has been a single team from the city which has played every National League season since, with no other major league rivals. Neither the American League nor the short-lived Federal League attempted to place a team in Cincinnati.

Mascot Mr. Redlegs

Early in the 20th century, the team was referred to in sports articles as "Redlegs" as well as "Reds." From 1954 to 1959, the team officially changed its name to the Cincinnati Redlegs to avoid confusion and possible association with the political "Reds" (Communists), which were especially controversial in the United States at the time.